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On the inside of the left crank there is a small ring. The picture shows where the ring is meant to go.

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The ring is smooth / flat on one side. The picture shows the flat side which seems to have been rubbed silver by friction. The flat side seems to be made of metal.

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The other side has a raised ridge on the inner circumference. The raised ridge has a rubber/ plastic feel.

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What is the correct way to install this ring?

(Please excuse the low resolution images. It's the best this phone can do.)


Update

It's possible that I previously installed this ring the wrong way and that's perhaps why the one side is polished. The ring seems to fit best with the ridged-side towards the bearing.

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    Not an answer but logic would say: friction polished side towards bearing.
    – Carel
    Jan 9 '19 at 19:33
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    The exploded view of an octaink crank from the Shimano Manuals and Technical documents website (si.shimano.com/#) just show a washer flat on both sides. The drawings here are not super high quality but...and a couple "Dealer's Manuals" do not reference this aspect at all. The right side should also have a washer undernealth the fixing bolt. Perhaps check the shape and direction of this one you have.
    – Jeff
    Jan 11 '19 at 5:23
  • @Jeff Octalink is very different from Hollowtech II with bearings elsewhere (internal vs. external) and with cranks being fixed in a very different way (crank integrated vs. bb integrated axle).
    – Vladimir F
    Jan 15 '20 at 15:40
  • @Vladimir F Quite so regarding the cartridge bearing octalink vs. the external bearings of HT2. Being several months ago, I cannot say now why I interpreted the question as referring to the washer of an octalink's crankarm fixing bolt, which obviously it is not. I suspect I did not pay close attention to the photo of the crank arm and on looking at the washer photos, concluded it was the fixing bolt washer of a cartridge bearing crank, which also is two-sided and very similar looking to the photos. Except in size of course, which was another poor observation by me.
    – Jeff
    Jan 17 '20 at 9:04
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The side that you say has been rubbed silver by friction is like that on a new ring (I've got two, bought from SJS cycles). From what I can tell from other posts it's intended to stop water and crud getting into the bearing. That would suggest that the non-silver side, the ridged side, should go next to the bearing because this is like an oil seal (although there appears to be no rotational movement between the two). The silver side goes into the recess on the crank arm. The washer is a tightish (waterproof) fit on the spindle so together this should stop water getting into the bearing from the spline on the crank arm.

Just to clarify, there is probably no rotational movement between the crank arm and the face of the bearing - the inner part of the bearing appears to be free to rotate with the arm and the spindle. However, there must be a seal within the bearing to seal the rotating inner part from the fixed outer part.

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